HindawiBioMed Research InternationalVolume 2018, Article ID 4246874, 7 pages StudyThe Influence of the Crown-Implant Ratio on the Crestal BoneLevel and Implant Secondary Stability: 36-Month Clinical StudyJakub Hadzik ,1,2 Maciej Krawiec,1 Konstanty SBawecki,1 Christiane Kunert-Keil ,3Marzena Dominiak,1 and Tomasz Gedrange 1,31Department of Dental Surgery, Wroclaw Medical University, ul. Krakowska 26, 50-425 Wrocล‚aw, PolandDepartment of Oral Implantology, Wroclaw Medical University, ul. Krakowska 26, 50-425 Wrocล‚aw, Poland3Department of Orthodontics, Technische Universitaฬˆt Dresden, Carl Gustav Carus Campus, Fetscherstr. 74, 01307 Dresden, Germany2Correspondence should be addressed to Jakub Hadzik; [email protected] 21 January 2018; Accepted 4 April 2018; Published 16 May 2018Academic Editor: Gilberto SammartinoCopyright 2018 Jakub Hadzik et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Introduction. When the era of dental implantology began, the pioneers defined some gold standards used in dental prostheticstreatment for implant-supported restorations. Referring to traditional prosthetics, it was taken for granted that the length of animplant placed in the alveolar bone (the equivalent of the root) should exceed the length of the superstructure. Aim of the Study. Theaim of the study was to determine whether implant length and the crown-to-implant (๐ถ/๐ผ) ratio influence implant stability and theloss of the surrounding marginal bone and whether short implants can be used instead of sinus augmentation procedures. Materialand Methods. The patients participating in the study (๐‘› 30) had one single tooth implant, a short (OsseoSpeed L6 ร˜4 mm,Implants) or a regular implant (OsseoSpeed L11 and L13 ร˜4 mm, DENTSPLY Implants), placed in the maxilla. The evaluationwas based on clinical and radiological examination. The crown-to-implant ratio was determined by dividing the length of thecrown together with the abutment by the length of the implant placed crestally. Mean crown-to-implant ratios were calculatedseparately for each group and its correlation with the MBL (marginal bone loss) and stability was assessed. The authors comparedthe correlation between the ๐ถ/๐ผ ratio values, MBL, and secondary implant stability. Results. Positive results in terms of primaryand secondary stability were achieved with both (short and conventional) implants. The MBL was low for short and conventionalimplants being 0.34 0.24 mm and 0.22 0.46 mm, respectively. No significant correlation was found between the ๐ถ/๐ผ ratio andsecondary stability as well as the ๐ถ/๐ผ ratio and the marginal bone loss. Conclusions. Short implants can be successfully used tosupport single crowns. The study has revealed no significant differences in the clinical performance of prosthetic restorationssupported by short implants. Clinical trial registration number is NCT03471000.1. IntroductionThe crown-to-root (๐ถ/๐‘…) ratio is commonly used by dentalclinicians to qualify a tooth for a fixed dental crown. Itis believed that a proper ๐ถ/๐‘… is one of the key factors inachieving a long-term prognosis in prosthetic rehabilitation[1โ€“3]. The importance of a proper ๐ถ/๐‘… ratio may be explainedby the biomechanical concept of a class I lever, so whena disproportionate ๐ถ/๐‘… ratio occurs, the periodontium ismore susceptible to injury due to heavy occlusal forces. Thisphenomenon was studied, for example, by McGuire andNunn in a prospective study on predicting tooth loss forperiodontal patients [4]. There are no strict guidelines for a๐ถ/๐‘… ratio, but when a periodontium is healthy the optimal๐ถ/๐‘… ratio for a fixed crown is considered 1 : 2 or less [1, 5].When the era of dental implantology began, cliniciansstarted using certain guidelines associated with natural teethfor the implant-supported fixed crowns. It was taken forgranted that the length of an implant placed in the alveolarbone (the equivalent of the root) part should exceed thelength of the superstructure.Many studies have shown that the success of implantosseointegration is considerably dependent on its surfaceand it has been proven that osteoblastic cells adhere morequickly to rough surfaces [6โ€“8]. Many methods for increasingthe dental implant roughness were described; one of them

2is the the sandblasted and acid-etched surface created bythe combination of sand-blasting and acid-etching is themost relevant and most commonly used method, and itssignificance has been documented in numerous studies [9โ€“11].Before implant surface modifications were widely recognized in the literature, in case of insufficient bone volume,augmentation procedures had been the only solution toensure sufficient bone volume [12]. In the maxilla, in caseswith vertical dimension deficiency, the augmentation in themaxillary sinus prior to the planned implantation is oftennecessary to obtain sufficient bone volume to stabilize adental implant. Many biomaterials (including autografts,allografts, xenografts, and alloplasts) may be successfullyused in these techniques, but sinus lift procedures featurethe risk of complications, such as the perforation of theSchneiderian membrane (7โ€“30% depending on the usedtechnique and instruments) [13โ€“15].The indisputable progress and improvement of theimplant surface enabled implant length reduction while stillmaintaining proper stability and functionality. Short implantscould be used in cases where traditional implants preceded bythe grafting procedure were the only solution. Furthermore,the implant surface modification also made it possible to stopfollowing the guidelines used in traditional prosthetics. Thebarrier to maintaining a proper crown-to-implant (๐ถ/๐ผ) ratiowas exceeded. A considerable number of studies addressedthe issue of implant length as a predictor of implant survival,but they achieved inconclusive results. However, it has beenpointed out that the excessive ๐ถ/๐ผ ratio could impair longterm implant survival [16].On the other hand, the recent literature indicates verypromising results and argues that short implants may safelyreplace regular implants; however, due to their sophisticatedsurface, short implants remain stable when loaded with acrown longer than the implant itself [17โ€“19].The aim of the study was to check whether the crownimplant ratio influences the secondary implant stability andthe marginal bone level [MBL] in implants loaded withsingle nonsplinted crowns. It was also assessed whether theuse of increased ๐ถ/๐ผ ratios for short implants would be assuccessful as for long implants proceeded by maxillary sinusaugmentation with a xenograft.2. Material and MethodsFor the purpose of unifying the nomenclature in themanuscript, authors use the word superstructure for theprosthetic crown with the abutment.2.1. Experimental Design. This prospective study was conducted based on clinical and radiographic examination. Thestudy protocol was approved by the local ethical commission (Bioethics Committee at Wroclaw Medical University,approval number KB 427/201). All patients gave two writtenconsents: the first was general consent to have dental implantsplaced, and the other consent involved the participation inthe study. The study has been conducted in full compliancewith the Declaration of Helsinki. The primary protocol ofBioMed Research Internationalthe study assumed a larger group of patients; however, only30 patients were included in this long follow-up period.Other patients because of long evaluation period resignedfrom participation in the project; others because of poorcompliance were excluded from the project.The evaluation in this study group of patients incorporated 30 adults (10 males, 20 females), with a mean ageof 45.5 years, who had DENTSPLY implants placed at theDepartment of Dental Surgery at Wroclaw Medical University. The patients who met the inclusion criteria were dividedat random (by drawing lots) into two groups according to themethod of treatment provided.Group 1 (G1; ๐‘› 15 patients) had conventionaldental implants (OsseoSpeed L11 ร˜4 mm and L13 ร˜4 mm)[DENTSPLY Implants, Waltham, MA, USA] placed, preceded by the sinus lift procedure from a lateral windowapproach with the application of the xenogeneic bone graftGeistlich Bio-Oss [Geistlich AG, Wolhusen, Switzerland].The lateral window approach sinus lift surgery was performed6 weeks prior to the implant placement by the same surgeon.Group 2 (G2; ๐‘› 15 patients) had short implants(OsseoSpeed L6 mm ร˜4 mm) [DENTSPLY Implants, Waltham, MA, USA] placed without sinus lift and augmentationprocedure.2.2. Inclusion and Exclusion Criteria. Nonsmoking patientswith no systemic or local diseases were qualified.Additional inclusion criteria were as follows:(i) Minimal apicocoronal height of the alveolar ridge of6 mm in the region of the implant insertion in thepresurgical qualification(ii) Minimal width of the alveolar ridge of 6-7 mm in theregion of interest(iii) HKT (height of the keratinized tissue) higher than2 mm(iv) API 35 (Approximal Plaque Index)(v) PI 25. (Plaque Index)(vi) Bone Type III or D2 were included in the study(vii) No graft procedures in the area of interestIn both groups, D2 (Misch) was the radiologically andclinically assessed bone density based on presurgery CT scansand intrasurgery clinical evaluation. The surgical procedurewas performed under the same conditions and by the samemedical team with induced local anesthesia. All patients wereinstructed to rinse their mouths with 0.12% chlorhexidinesolution (twice a day until suture removal) and to takethe prescribed antibiotics and analgesics (Augmentin 1,0 intabl. One dose at one hour before the surgery and then5 days after implant placement 1,0 g every 12 hours). Inaddition patients in Group 1 where the sinus floor waselevated received additional antibiotic therapy when thesurgery was performed (Augmentin 1,0 in tabl. One dose atone hour before the surgery and then 5 days after implantplacement 1,0 g every 12 hours). Nonresorbable sutures wereremoved 7โ€“14 days after the implant placement. In all cases,

BioMed Research Internationalfinal restorations were manufactured and cemented withresin based semipermanent cement 6 months after implantplacement. All implants in this study were loaded with singlenonsplinted crowns.CBCT (Cone Beam Computed Tomography) [Galileos D3437, Sirona Dental, Germany] and RVG [Visualix eHD,Gendex Dental Systems, USA] were taken for each implantanalyzed and measured to assess the crown-implant ratio. Theinitial CBCT and RVG taken immediately after the implantplacement (T0) and CBCT and RVG radiographs taken after36 month (T1) were used to assess the marginal bone levelchanges. The loss of the marginal bone was measured basedon the CBCT image and using a standard RVG periapicalX-ray done with the use of a straight angle technique witha positioner. The CBCT image offers transrectal views sothe measurement can be made around the implant. On theperiapical X-ray, the bone level was measured on the mesialand distal site of the implant and the mean values werecalculated. The measuring points on CBCT were locatedaround the implant (4 points around each mesial, distal,buccal, and palatal) and the mean values were calculated.To indicate the value in millimeters, in each case the radiological measurement was calibrated with the previouslyknown length of the implant. Then the mean value of themeasurements from both CBCT and RVG was calculated andthese mean values were presented in the manuscript.For Periotest , measured in PVT Periotest Values [Periotest Classic, Medizintechnik Gulden, Germany] examination was performed to assess secondary implant stabilityafter 36 months. In all cases, the Periotest evaluation wasconducted in the same manner. Each implant was evaluatedat 4 different location points, each with a different directionof the excitation: 2 points at the buccal (45 degrees from themesiobuccal direction, 90 degrees from the buccal direction,both at the half the height of the supragingival part of thecrown) and similarly on the palate, each excitation place wasevaluated 3 times. The mean was calculated for all evaluationpoints for each implant.The crown-to-implant ratio was determined by dividingthe length of the superstructure (crown and the abutment) bythe length of the implant that was placed crestally (Figures 1and 2). Mean crown-to-implant ratios were calculated separately for each group and its correlation with the MBL (MBL marginal bone loss) and implant stability was evaluated.The authors compared the correlation between the range of๐ถ/๐ผ ratio values, the MBL, and secondary implant stability,respectively.2.3. Statistical Analysis. The statistical analysis was performed using GraphPad Prism 6 software [GraphPad Software, Inc., USA]. Spearmanโ€™s rho test was used to measurecorrelation. All data were given as means standard deviation (SD). ๐‘ƒ 0.05 was considered statistically significant.3Figure 1: Periapical digital radiograph of a short implant (Astra Techimplant system OsseoSpeed TX 4.0 S; ร˜4 mm, 6 mm long). The๐ถ/๐ผ ratio measurement method is presented. Radiological status 36months after implant placement.Figure 2: Periapical digital radiograph of a regular implant (AstraTech implant system OsseoSpeed TX 4.0 S; ร˜4 mm, 11 mm long).The ๐ถ/๐ผ ratio measurement method is presented. Radiological status36 months after implant placement.1.0 2.7 PTV). The marginal bone level loss was low andsimilar in both groups (G1 and G2: 0.22 0.46 mm and 0.34 0.24 mm). No significant difference in the MBL between shortand regular implants was found (Table 1).The average ๐ถ/๐ผ ratio in G1 was 1.063 and in G2 1.69(Table 2). No significant correlation between the ๐ถ/๐ผ ratioand the secondary stability was found as well as for the ๐ถ/๐ผratio and the marginal bo